European leaders meet tonight to thrash out a pledge to come to the rescue of Greece for the second time in 15 months.

The Brussels summit of the EU's heads of government was scheduled to focus on the European economy, immigration policy and upheavals in the Middle East, but has been overshadowed by the sovereign debt crisis in Greece, which is perceived to be on the brink of a meltdown that might even trigger a renewed international banking crisis.

As Washington and the International Monetary Fund pile the pressure on EU leaders to deal decisively with the Greek emergency, the summit is expected to deliver a statement guaranteeing a second bailout later this year, worth up to €120bn, provided that the embattled government in Athens can meet its side of the bargain – secure parliamentary passage by next week of a draconian austerity package comprising €50bn worth of privatisations and €28bn of spending cuts and tax increases.

The new Greek finance minister, Evangelos Venizelos, unveiled details of the measures, which include lowering the minimum threshold for income tax to €8,000 a year from its current level of €12,000.

Greece will also levy a one-off solidarity tax ranging from 1-5% depending on income, increase tax on heating fuel, and impose a minimum tax on the self-employed, who are widely regarded as some of the country's most flagrant tax evaders.

To try to ease Greece's plight, José Manuel Barroso, the European commission president, will go the summit pleading with EU governments to agree to fast-track around €1bn from the EU budget to Greece for poverty and unemployment relief. If prime minister George Papandreou is fighting for his political life, the opposition leader, Antonis Samaras, has also come under intense pressure from EU leaders to line up behind his political enemies for the sake of the nation.

At a meeting of European centre-right leaders in Brussels today ahead of the summit, Germany's Chancellor Angela Merkel and others pressed Samaras to drop his bitter opposition to Papandreou and to support the austerity package in parliament. Samaras has sworn to oppose the measures, and his New Democracy party voted unanimously against Papandreou in a vote of confidence early on Wednesday morning.

The EU, the IMF and the European Commission all insist that the Greek austerity package has to be carried by the broadest possible majority next week.

In July and August, Greece has to redeem government bonds to the tune of €9.4bn. Without €12bn from the eurozone and the IMF – the fifth tranche of last year's €110bn bailout – by mid-July, Greece will be broke, bringing about a sovereign default and a bigger international crisis.

The IMF has told the EU it will not pay up in July unless the Greek austerity measures are agreed and unless it has cast-iron guarantees from the eurozone on a second three-year bailout of a similar scale to last year's.

"For programmes which extend beyond the next election date, the IMF values cross-party support to ensure the sustainability of the programme," said a senior German government official. "IMF participation is a condition for our participation in a Greek [rescue] package."

The Greek parliament has to endorse the austerity package next week. Then an emergency meeting of eurozone finance ministers on 3 July is to hammer out the details of the new bailout. Then the IMF, under the likely new leadership of Christine Lagarde, the French finance minister, is to hold a board meeting on 8 July before agreeing to disburse its part of the €12bn by 15 July.

The granting of the €12bn would provide a breathing space and give the eurozone until September to sign off on the new three-year rescue deal.

In the meantime, EU governments are negotiating with Greece's private creditors, asking them to volunteer to roll over whatever debt becomes due between now and 2014. This would reduce the size of the bailout required, but it is not clear by how much.

Prime minister David Cameron will go into the summit pressing for decisive action by eurozone leaders, but determined to avoid taking part in the European side of the new bailout. His success will depend on how strongly Germany insists on using a European Commission-administered fund, for which Britain is partly liable, for part of the proposed rescue.

Cameron does not have a veto over the decision and a German law from last year on the EU's temporary bailout measures stipulates that the commission fund should be used.